MRI has been used to evaluate the change (deformation) of articular cartilage immediately after knee- loading. This novel approach may represent in vivo measure of the functional capacity of cartilage, and has been applied primarily in studies of young persons with healthy knees. Deformation post-loading may be more pronounced in OA cartilage. We propose to test two primary hypotheses: 1) the magnitude of tibiofemoral (TF) and patellofemoral (PF) cartilage deformation after a knee-loading protocol is greater in OA knees than knees from age- and gender-matched control participants without knee OA; 2) in persons with knee OA, greater malalignment is associated with greater cartilage deformation after loading. Secondarily, we will: examine whether cartilage lesions (i.e. new, transient lesions or worsening of existing lesions) after knee loading are more common in OA knees than knees of persons without knee OA; and examine, among those with knee OA, the relationship of deformation to age, gender, BMI, OA disease severity, medial-lateral laxity, physical activity, and muscle strength. Our current proposal will capitalize on the infrastructure of the Mechanical Factors in Arthritis of the Knee (MAK) study ongoing at our institution. [unreadable] [unreadable] [unreadable]